The aim of this study was to evaluate an efficiency of clay minerals (kaolinite, illite, Na- and Ca-montmorillonite) in alleviating the water repellency of stearic acid sand during the course of long-term hot and dry spell. This spell was simulated by prolonged drying (incubation) of the samples in oven at 50°C. It was found that the kaolinite addition resulted in a drop in the persistence of water repellency of the stearic acid sand. On the contrary, the Ca-montmorillonite addition increased markedly the persistence of water repellency of the stearic acid sand. In most cases, the illite addition resulted in an increase in the persistence of water repellency, even though not so markedly as it was in the case of Ca-montmorillonite addition. In the case of Na-montmorillonite addition, the striking drop in the persistence of water repellency of the stearic acid sand was registered only after lowering the moisture below 5 %. An increase in the persistence of water repellency of the sand-clay mixture with an increase in the clay amount is another interesting finding, observed in case of kaolinite and Ca-montmorillonite. and Cieľom tejto štúdie bolo zhodnotenie efektívnosti ílových minerálov (kaolinitu, illitu, Na- a Camontmorillonitu) pri znižovaní stálosti vodoodpudivosti piesku pokrytého kyselinou stearovou počas dlhého suchého a teplého obdobia, simulovaného inkubáciou vzoriek pri teplote 50 °C. Zistili sme, že pridanie kaolinitu výrazne znížilo stálosť vodoodpudivosti piesku pokrytého kyselinou stearovou prakticky počas celého cyklu sušenia. Pridanie Ca-montmorillonitu naopak stálosť vodoodpudivosti piesku pokrytého kyselinou stearovou výrazne zvýšilo. Pridanie illitu vo väčšine prípadov zvýšilo stálosť vodoodpudivosti piesku pokrytého kyselinou stearovou, aj keď nie tak výrazne ako pridanie Ca-montmorillonitu. V prípade pridania Na-montmorillonitu sme výrazné zníženie vodoodpudivosti piesku pokrytého kyselinou stearovou zaznamenali až po poklese vlhkosti vzorky pod 5 %. Ďalším zaujímavým poznatkom je vzrast vodoodpudivosti so zvyšujúcim se obsahom ílu, ktorý sme zaregistrovali v prípade kaolinitu a Ca-montmorillonitu.
The extent (determined by the repellency indices RI and RIc) and persistence (determined by the water drop penetration time, WDPT) of soil water repellency (SWR) induced by pines were assessed in vastly different geographic regions. The actual SWR characteristics were estimated in situ in clay loam soil at Ciavolo, Italy (CiF), sandy soil at Culbin, United Kingdom (CuF), silty clay soil at Javea, Spain (JaF), and sandy soil at Sekule, Slovakia (SeF). For Culbin soil, the potential SWR characteristics were also determined after oven-drying at 60°C (CuD). For two of the three pine species considered, strong (Pinus pinaster at CiF) and severe (Pinus sylvestris at CuD and SeF) SWR conditions were observed. Pinus halepensis trees induced slight SWR at JaF site. RI and RIc increased in the order: JaF < CuF < CiF < CuD < SeF, reflecting nearly the same order of WDPT increase. A lognormal distribution fitted well to histograms of RIc data from CuF and JaF, whereas CiF, CuD and SeF had multimodal distributions. RI correlated closely with WDPT, which was used to develop a classification of RI that showed a robust statistical agreement with WDPT classification according to three different versions of Kappa coefficient.
This study tested the hypothesis that the changes in hydrophysical parameters and heterogeneity of water flow in an aeolian sandy soil have the same trend as the process of succession. Three sub-sites were demarcated at the area of about 50 m x 50 m. The first sub-site was located at the pine-forest glade covered with a biological soil crust and represented the initial stage of succession. The second sub-site was located at the grassland and represented more advanced stage of succession. The third sub-site was located at the pine forest with 30-year old Scots pines and represented advanced stage (close to climax) of succession. The sandy soil at the surface was compared to the soil at the pine-forest glade at 50 cm depth, which served as a control because it had a similar texture but limited impact of vegetation or organic matter. It was found that any type of vegetation cover studied had a strong influence on hydrophysical parameters and heterogeneity of water flow in an aeolian sandy soil during hot and dry spells. The changes in some hydrophysical parameters (WDPT, R, k(-2 cm), Sw(-2 cm), ECS and DPF) and heterogeneity of water flow in an aeolian sandy soil had the same trend as the process of succession, but it was not so in the case of Ks and Se(-2 cm), probably due to the higher content of smaller soil particles in grassland soil in comparison with that content at other sub-sites. Both the persistence and index of water repellency of pure sand differed significantly from those of grassland, glade and forest soils. The highest repellency parameter values in forest soil resulted in the lowest value of both the water sorptivity and hydraulic conductivity in this soil in comparison with other soils studied. The highest value of ethanol sorptivity and the lowest value of saturated hydraulic conductivity in the grassland soil in comparison with other soils studied were due to the higher content of fine-grained (silt and clay) particles in the grassland soil. The effective cross section and the degree of preferential flow of pure sand differed significantly from those of grassland, glade and forest soils. The change in soil hydrophysical parameters due to soil water repellency resulted in preferential flow in the grassland, glade and forest soils, while the wetting front in pure sand area exhibited a form typical of that for stable flow. The latter shape of the wetting front can be expected in the studied soils in spring, when soil water repellency is alleviated substantially., The columnar shape of the wetting front, which can be met during heavy rains following long dry and hot spells, was attributed to redistribution of applied water on the surface to a series of micro-catchments, which acted as runon and runoff zones., V príspevku sa testovala hypotéza, že zmeny hydrofyzikálnych parametrov a heterogenita prúdenia vody v piesočnatej pôde majú rovnaký trend ako proces sukcesie. Na ploche asi 50 m x 50 m sa vytýčili tri parcely. Prvá parcela sa nachádzala na čistine pokrytej biologickým pôdnym pokryvom a reprezentovala počiatočné štádium sukcesie. Druhá parcela sa nachádzala na zatrávnenej ploche a reprezentovala rozvinutejšie štádium sukcesie. Tretia parcela sa nachádzala v borovicovom lese a reprezentovala rozvinuté štádium sukcesie (blízke ku klimaxovej vegetácii). Piesočnatá pôda na povrchu parciel sa porovnávala s pôdou z čistiny v hĺbke 50 cm, ktorá slúžila ako kontrola, pretože mala skoro rovnakú textúru, avšak veľmi malý vplyv vegetácie alebo organickej hmoty. Zistili sme, že akýkoľvek typ študovaného vegetačného pokryvu mal veľký vplyv na hydrofyzikálne parametre a heterogenitu prúdenia vody v piesočnatej pôde počas horúcich a suchých období. Zmeny niektorých hydrofyzikálnych parametrov (WDPT, R, k(-2 cm), Sw(-2 cm), ECS a DPF) a heterogenity prúdenia vody v piesočnatej pôde mali rovnaký trend ako proces sukcesie, neplatilo to však v prípade Ks a Se(-2 cm), pravdepodobne v dôsledku vyššieho obsahu malých pôdnych častíc v pôde s trávnatým pokryvom v porovnaní s inými parcelami. Stálosť aj index vodoodpudivosti čistého piesku sa štatisticky významne líšili od hodnôt týchto parametrov v pôde pod trávou, biologickým pôdnym pokryvom a borovicami. Najvyššie hodnoty parametrov vodoodpudivosti v tráve pod borovicami mali za následok najnižšie hodnoty sorptivity pre vodu a hydraulickej vodivosti v tejto pôde v porovnaní s ostatnými študovanými pôdami. Najvyššie hodnoty sorptivity pre etanol a najnižšie hodnoty nasýtenej hydraulickej vodivosti v pôde pod trávou v porovnaní s inými pôdami boli pravdepodobne spôsobené vyšším obsahom malých pôdnych častíc v tejto pôde. Efektívny prierez (ECS) a stupeň preferovaného prúdenia (DPF) čistého piesku sa štatisticky významne líšili od hodnôt týchto parametrov v pôde pod trávou, biologickým pôdnym pokryvom a borovicami. Zmeny hydrofyzikálnych parametrov pôdy v dôsledku jej vodoodpudivosti mala za následok preferované prúdenie v pôde pod trávou, biologickým pôdnym pokryvom a borovicami, zatiaľ čo čelo omáčania v čistom piesku malo tvar typický pre stabilné prúdenie. Takýto tvar čela omáčania možno vo všetkých študovaných pôdach očakávať na jar, keď je vodoodpudivosť pôdy podstatne znížená v dôsledku jej zvýšenej vlhkosti., and Čelo omáčania v tvare prstov, ktoré možno očakávať počas prívalových dažďov nasledujúcich po dlhých suchých a horúcich obdobiach, možno pričítať redistribúcii vody na povrchu pôdy do viacerých mikropovodí, ktoré sa správali ako vtokové a odtokové oblasti
The aim of this study was to determine the potential development of water sorptivity of soil aggregates by heating. Soil aggregates were sampled from arable layer of 5 Polish soils: Haplic Luvisol 1 from Czesławice, Haplic Luvisol 2 from Wierzchucinek, Haplic Cambisol from Felin, Gleyic Mollic Cambisol from Chylice, and Haplic Phaeozem from Grabiec. Three aggregates of each soil type with minimum diameter between 4 and 10 mm were heated in the oven for at least 3 hours at temperatures 20, 100, 200, 250, and 360ºC. After each temperature treatment the soil aggregates were conditioned at the room temperature for 16 hours. Laboratory measurements of water sorptivity of soil aggregates were performed under a negative tension h0 = -2 cm using tension infiltrometer. It was found that the exposure to temperatures between 100 and 200°C tends to decrease water sorptivity of aggregates from all the studied soils but one (Haplic Luvisol 1), followed by about two- to four-fold increase in water sorptivity for exposure to temperatures of 250°C (in Haplic Luvisol 1, Haplic Luvisol 2, and Haplic Phaeozem) or 360°C (in Haplic Cambisol and Gleyic Mollic Cambisol).
Water repellency is a relative (and a little misleading) term because no surface actually exerts a repelling force on a liquid. There is always some attraction between a liquid and any solid. The affinity (hydrophilicity) or repellency (hydrophobicity) between water and solid surfaces originates from mutual attractive forces (adhesion) and the attraction between the water molecules (cohesion). Soil water repellency is generally attributed to hydrophobic organic matter coating soil particles or accumulating in the soil environment. The definition of hydrophobicity and hydrophilicity, based on the contact angle α between water and a solid, reads: if α < 90°, the solid is wettable, if α ≥ 90°, the solid is water repellent (Adamson, 1990). Another definition of hydrophobicity and hydrophilicity, based on the surface-free energy, reads: solid surfaces with a surface-free energy σsa > 72.75 mN m-1 attract water and are therefore hydrophilic. Solid surfaces with a surface-free energy σsa < 72.75 mN m-1 are hydrophobic (Doerr et al., 2000). Soil water repellency (WR) is characterised using three parameters: severity (degree) of WR, persistence of WR, and index of WR. The most frequently used techniques for the severity and persistence of WR measurements are MED (molarity of ethanol droplet) and WDPT (water drop penetration time) test, respectively. and Vodoodpudivosť je relatívny (a trochu zavádzajúci) pojem, pretože žiadny povrch tuhej látky nepôsobí na kvapalinu odpudivou, ale vždy príťažlivou silou. Afinita (hydrofilnosť) alebo odpudivosť (hydrofóbnosť) medzi vodou a povrchom tuhej látky vzniká zo vzájomných príťažlivých síl (adhézia) a príťažlivých síl medzi molekulami vody (kohézia). Vodoodpudivosť pôdy sa všeobecne pripisuje hydrofóbnej organickej hmote, ktorá buď pokrýva pôdne častice alebo je akumulovaná v pôdnom prostredí. Definícia hydrofóbnosti a hydrofilnosti, založená na veľkosti uhla omáčania, znie: ak je uhol omáčania α menší ako 90°, tuhá látka je zmáčavá, ak je väčší alebo sa rovná 90°, tuhá látka je vodoodpudivá (Adamson, 1990). Iná definícia hydrofóbnosti a hydrofilnosti, založená na povrchovej voľnej energii, znie: povrch tuhej látky s povrchovou voľnou energiou σsa > 72,75 mN m-1 je hydrofilný a povrch tuhej látky s povrchovou voľnou energiou σsa < 72,75 mN m-1 je hydrofóbny (Doerr et al., 2000). Vodoodpudivosť je charakterizovaná tromi parametrami: veľkosť, stálosť a index vodoodpudivosti. Najčastejšie používanou metódou na meranie veľkosti vodoodpudivosti pôdy je MED test, v ktorom sa povrchová voľná energia pôdy určuje z molarity kvapky etanolu, ktorá vnikne do pôdy za určitý čas. Najčastejšie používanou metódou na meranie stálosti vodoodpudivosti pôdy je WDPT test, pri ktorom sa meria čas, potrebný na infiltráciu kvapky destilovanej vody do pôdy.
The main hydrological and geomorphological impacts of soil water repellency are: (a) reduced infiltration capacity; (b) increased overland flow; (c) spatially localised infiltration and/or percolation, often with fingered flow development; (d) effects on the three-dimensional distribution and dynamics of soil moisture, evapotranspiration, as well as plant germination and growth; (e) enhanced streamflow responses to rainstorm; (f) enhanced total streamflow; and (g) enhanced soil erosion. Surfactants (wetting agents), clay, and municipal solid waste compost were found to be successful in mitigation of the consequences of soil water repellency. and Hlavné hydrologické a geomorfologické dôsledky vodoodpudivosti sú: (a) zmenšenie rýchlosti infiltrácie vody do pôdy, (b) zväčšenie povrchového prúdenia, (c) priestorovo lokalizovaná infiltrácia a/alebo perkolácia a prúdenie prstami, (d) účinky na trojrozmerné rozdelenie a dynamiku pôdnej vlhkosti, evapotranspiráciu, ako aj klíčenie a rast rastlín, (e) zväčšenie odtoku po búrke, (f) zväčšenie celkového odtoku a (g) zväčšenie erózie pôdy. Dôsledky vodoodpudivosti pôdy možno zmierniť aplikáciou povrchovo aktívnych látok (zmáčadiel), ílu a kompostu z tuhého komunálneho odpadu.